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IAUC 5259: 1991Y; N Mus 1991; 1991T

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                                                  Circular No. 5259
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     J. Mueller reports her discovery of an apparent supernova (mag
about 19) in a galaxy located at R.A. = 17h13m.7, Decl. = +57 22'
(equinox 1950.0) on a blue plate taken Apr. 17 UT by C. Brewer and
herself with the 1.2-m Oschin Telescope in the course of the second
Palomar Sky Survey.  The object is located 7" north of the galaxy
center.  N. Reid reports that a blue Sky Survey plate taken 1990 Apr.
22 by Brewer and J. D. Mendenhall shows no object at this position.

     C. Bailyn, Astronomy Department, Yale University, reports:  "V-
and B-band photometry of the optical counterpart of GRS 1121-68
(IAUC 5165) with the Cerro Tololo Interamerican Observatory 0.9-m
telescope (+ CF/CCD) reveals regular luminosity variations on a
10.5-hr timescale.  The variations take the form of a 3-hr rise to a
maximum 0.2 magnitude brighter than the quiescent level of V = 15.0,
followed by a similar decline.  The nova was observed for most of
the nights of Apr. 21-25, during which maximum brightness occurred
on Apr. 21.161, 22.035, 24.232, and 25.105 UT.  There are night-to-
night variations in the lightcurve shape, and occasional superposed
dips of a few hundredths of a magnitude lasting about 20 min.  The
10.5-hr modulation might be due to a hot spot, in which case the
observed period would be the orbital period.  Alternatively, the
modulatation might be caused by behavior analogous to the superhumps in
SU UMa stars (as suggested for GS 2000+25 by Charles et al. 1991,
MNRAS 249, 567), in which case the observed period would be a few
percent longer than the orbital period.  No color change is
observed, which supports the latter interpretation."

     Corrigenda.  On IAUC 5251, line 14,  for  1975 km/s  read  1775
km/s; on lines 15-16,  for  9770 and 15 000 km/s  read  9570 and
14 900 km/s
     Visual magnitude estimates (cf. IAUC 5255):  May 1.52 UT, 11.7
(A. Pearce, Scarborough, W.A.); 1.89, 11.6 (P. Schmeer, Bischmisheim,
Germany); 2.21, 11.2 (A. Hale, Las Cruces, NM); 3.22, 11.3 (W. Wren,
near Fort Davis, TX); 4.17, 11.4 (D. W. E. Green, Harvard, MA);
5.07, 11.6 (Green); 6.26, 11.6 (Wren).

1991 May 6                     (5259)             Daniel W. E. Green

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